1. Field of the Invention
The present invention relates to a battery (nonaqueous electrolyte secondary battery) including a nonaqueous electrolytic solution and a method of manufacturing the same.
2. Description of Related Art
The importance of nonaqueous electrolyte secondary batteries such as a lithium ion secondary battery has increased as a power supply, for example, a vehicle-mounted power supply or a power supply for a PC, a portable device, or the like. In particular, a lithium ion secondary battery is preferably used as a vehicle-mounted power supply with high output because it is light-weight and has high energy density. As a structure of such a battery, a battery structure is known including a nonaqueous electrolytic solution and a wound electrode body in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are laminated and wound together with a separator. From the viewpoint of obtaining high physical strength, a metal case is used as a battery case. In this case, typically, an electrode body is covered with an insulating film to insulate the battery case and the electrode body from each other. For example, Japanese Patent Application Publication No. 2006-278245 (JP 2006-278245 A) and Japanese Patent Application Publication No. 2009-026704 (JP 2009-026704 A) discloses batteries including an electrode body and a battery case, in which an insulating film is arranged between the electrode body and the battery case.
In the nonaqueous electrolyte secondary battery having the above-described configuration, a space between the positive electrode and the negative electrode (that is, an internal space of an electrode body) is filled with an appropriate amount of a nonaqueous electrolytic solution to realize the smooth movement of charge carriers between the electrodes. Therefore, when the liquid volume of the nonaqueous electrolytic solution held in (impregnated into) the electrode body is lower than a necessary volume (that is, when liquid shortage occurs), charge-discharge performance may deteriorate. For example, the shortage of the nonaqueous electrolytic solution may cause a decrease in cycle characteristics (a decrease in cycle characteristics caused by high-rate charging and discharging). Therefore, when the nonaqueous electrolyte secondary battery is used for an application in which charging and discharging are repeated at high input and output densities (for example, a vehicle-mounted battery in which high-rate charging and discharging is repeated) or for an application in which it is required that high battery performance can be exhibited for a long period of time (an application in which a long lifetime is required; for example, a vehicle-mounted battery which is generally used for 10 years or longer), it is strongly desired to prevent the shortage of the nonaqueous electrolytic solution.
In a nonaqueous electrolyte secondary battery in which a wound electrode body having a flat shape in a section perpendicular to a winding axis is accommodated in a quadrilateral battery case, a gap may be formed between a bottom-side R portion of the wound electrode body and a corner portion of the bottom of the battery case. From the viewpoint of impact resistance, the electrode body may be arranged in the battery case such that the top of the bottom-side R portion of the electrode body is separated from the bottom of the battery case. However, even with the above-described configuration, a gap is formed between the bottom-side R portion of the electrode body and the bottom of the battery case. The nonaqueous electrolytic solution held in this gap is not used for a cell reaction (movement of charge carriers between the electrodes). The nonaqueous electrolytic solution impregnated into the electrode body during battery construction may flow out from the electrode body during use of the battery. For example, electrode active materials contained in the positive electrode and the negative electrode may expand and contract due to repeated charging and discharging (in particular, high-rate charging and discharging) which forces the nonaqueous electrolytic solution outward from the inside of the electrode body. When the nonaqueous electrolytic solution flowing out from the electrode body is held in a gap between the bottom-side R portion of the wound electrode body and the bottom of the battery case, the amount of the nonaqueous electrolytic solution held in (impregnated into) the electrode body may be insufficient.